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Old 8th January 2013, 09:50 PM   #1521
jcx is offline jcx  United States
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Quote:
Originally Posted by gedlee View Post
I know of no literature that talks about thermal changes on a short time scale, only steady state SPL compression. If you know of such literature them please inform us.
no info on cycle-by-cycle compression at sound frequencies - but read what I said:

Quote:
and in fact the envelope modulation "compression" does occur on human perceptible time scales - if you have 10s of seconds attention span
the Klippel thermal modeling paper has plots labeled "measurement" that show ~ 100 C change in ~30 seconds - for the cooling curves

http://www.aes.org/tmpFiles/elib/20130108/5251.pdf from 1986 states that the voice coil thermal time constant can be less than 1 second...

I am certian I have read of people claiming to hear the thermal compression on successive envelope peaks in a musical phrase

Last edited by jcx; 8th January 2013 at 10:17 PM.
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Old 8th January 2013, 09:54 PM   #1522
gedlee is online now gedlee  United States
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Quote:
Originally Posted by weltersys View Post
One can certainly EQ anything flat at a low enough level, but if one actually wants high SPL low frequency, there are many useful specifications which will separate the wheat from the chaff.

Relevant specifications for a sub are frequency, phase, and impedance response, sensitivity, harmonic distortion at rated power, and power handling.
Phase? Really?

THD - you should know that I think this a completely useless specification.

Frequency response - you mean the response in a free field that has absolutely nothing to do with its response in a real room?

Impedance - sure, that's relevant, I can do that.

Power handling is what the driver manufacturer says it is.

You are quite correct that its the EQ capability that "will separate the wheat from the chaff" which is why I use drivers with headroom to spare. EQ is not going to be a problem in any small room.
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Old 8th January 2013, 09:55 PM   #1523
Omholt is offline Omholt  Norway
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I recently heard from somenone that B&C drivers have partially poor linearity and they exaggerate with the Xmax. Has anyone find this to be true?
Was recommended a BMS driver instead:
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Old 8th January 2013, 09:55 PM   #1524
gedlee is online now gedlee  United States
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Quote:
Originally Posted by jcx View Post
the Klippel thermal modeling paper has plots labeled "measurement" that show ~ 100 C change in ~30 seconds
That's "steady state" not "dynamic".
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Old 8th January 2013, 09:59 PM   #1525
gedlee is online now gedlee  United States
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Quote:
Originally Posted by Omholt View Post
I recently heard from somenone that B&C drivers have partially poor linearity and they exaggerate with the Xmax. Has anyone find this to be true?
The B&C woofer have ideally nonlinear BL vs x curves. Flat IS NOT what you want. A gradual falloff handles large excursions much better than a sharp falloff will. This is a very good reason why I prefer the B&Cs. This ideal that the BL should be flat is simply not true.

Low orders of distortion are not audible so its better to have a gradual BL falloff than a sharp one because the gradual one will sound cleaner at high levels. At low levels the two will sound the same.
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Old 8th January 2013, 10:56 PM   #1526
tinitus is offline tinitus  Europe
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they spec the voice coil length and magnet gap, so Xmax is easy to check
I had a look at a few woofers right now, and the their Xmax specs does seem a bit 'confusing' on some of them

but to be honest, some manufacturers do have errors in their spec sheets, as does the suppliers, etc etc
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Old 8th January 2013, 11:29 PM   #1527
gedlee is online now gedlee  United States
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There is no standard for "X-max" so its specification is all over the map.
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Old 8th January 2013, 11:33 PM   #1528
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Quote:
Originally Posted by gedlee View Post
The B&C woofer have ideally nonlinear BL vs x curves. Flat IS NOT what you want. A gradual falloff handles large excursions much better than a sharp falloff will.
Couldn't control under high excursion perhaps could be better handled by the driver's suspension? Some of the cleanest drivers I've heard (e.g. the Shiva X) have a pretty flat BL curve within their Xmax region.
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Old 8th January 2013, 11:35 PM   #1529
gedlee is online now gedlee  United States
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Quote:
Originally Posted by jcx View Post
I am certian I have read of people claiming to hear the thermal compression on successive envelope peaks in a musical phrase
Just as I am certain that no one has quantified this effect or discussed how or why one would want to control it. Both the Klippel paper and the Gander paper only deal with thermal compression, which, as I said and showed, is a different thing not highly correlated with thermal modulation because one is dominated by thermal dissipation, which the other is immune to.
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Old 8th January 2013, 11:40 PM   #1530
gedlee is online now gedlee  United States
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Quote:
Originally Posted by Brian Steele View Post
Couldn't control under high excursion perhaps could be better handled by the driver's suspension.
Best to do both because they effect different regions of the frequency response. Suspensions have no effect at and above resonance, but are quite effective below resonance. BL control works at and above resonance.
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